1. Technical Field
Embodiments of the present invention are directed to a wafer-level package for an optical sensor device, and in particular to a package in which a sensor assembly is embedded in a molding compound layer, and also to a camera module that includes such a package.
2. Description of the Related Art
A challenge that designers face with respect to coupling the optical sensor to a camera circuit is that the device must be positioned on a substrate with the optical sensor facing outward, and without any obstructions that would interfere with the reception of an optical image. It is therefore necessary to couple a circuit to contact pads that are not overlying the optical sensor using techniques that are often not compatible with the correct operation of the optical sensor. Additionally, as camera modules are more commonly used in small electronic devices such as cell phones and tablet computers, there is a strong market pressure to reduce the height of the modules so they can be installed in ever thinner devices.
FIG. 1 shows a known camera module 20 with a semiconductor die 22 on which an optical sensor circuit 26 is formed. The die 22 is mounted to a substrate 24 and wirebonds 28 couple the sensor circuit to a circuit in the substrate. A housing 30 covers the semiconductor die 22 and supports a lens barrel 32, which in turn supports a lens array 36 and a glass plate 34. The glass plate 34 commonly includes an infrared wavelength filter coating.
FIG. 2 shows another known camera module 40 that includes a semiconductor die 42 with an optical sensor circuit 26, a glass plate 52, a filter plate 56, and a lens housing 58 with a lens array 60. The semiconductor die 42 includes through-silicon vias (TSV) 48 that couple the sensor circuit 26 to a circuit on a support substrate 46. Legs 62 couple the housing to the underlying support substrate 46, and an array of solder balls 50 are provided to couple the module to a circuit board.
The example of FIG. 1 is problematic because the housing must be high enough and wide enough to accommodate the wirebonds 28, which makes it less desirable for use in small electronic devices because it limits the minimum thickness of such devices.
The example of FIG. 2 is an improvement over the previous example because it eliminates the wirebonds, which enables a more compact structure with a reduced height, meaning that the device in which it is mounted can be thinner than with the device of FIG. 1. Nevertheless, there are some problems associated with the configuration shown in FIG. 2, including the potential for light leaks. These problems and others will be discussed later.